Two-Dimensional Transient Modeling of Energy and Mass Transfer in Porous Building Components using COMSOL Multiphysics

This paper reports on a transient heat, air and moisture transfer (HAM) model. The governing partial-differential equations are simultaneously solved for temperature and capillary pressure through multi-layered porous media, including the non-linear transfer and storage properties of materials. Using partial differential equations functions, some thermo-physical properties of porous media are converted into coefficients depending on temperature and capillary pressure. Major features of the model are multi-dimensional and transient coupling of heat, air and moisture transport. The coupled equations are solved using the COMSOL Multiphysics time-dependent solver. This solver enables HAM (Heat, Air, Moisture) modeling in porous media. Besides, the good agreements obtained with a 2D benchmark suggest that the model can be used to assess the hygrothermal performance of building envelope components. This paper concludes that the total heat flux in the insulated wall represents only the quarter of that crossing the uninsulated concrete roof. On the other hand, the concrete having the lowest water vapour permeability of all used materials allows maintaining the vapour pressure levels close to the initial value (103 Pa). This induces a situation of interstitial condensation within the concrete of the roof. Being able to evaluate the hygrothermal behaviour, the proposed model may turn out to be a valuable tool to solve other building problems.